Mammography is a well-established method of breast imaging. Using mammograms of the breast, radiologists identify areas suspicious of pathologies. Further identification, such as the determination of cancer is usually done through the taking of a breast biopsy. This is done in several ways. One way is to use mammography to place a wire or needle into the breast, marking the suspected pathology's location. The patient then undergoes an open surgical procedure, and the surgeon can remove tissue from the suspicious area marked by the wire or needle. This is an open surgical biopsy. Another method is known as stereotactic breast biopsy. In this method, using image guidance, a hollow needle is inserted into the breast, and a tissue sample is taken from the area of interest, without a separate surgical procedure. As stated above both methods require some method of localization of the area of interest and a method to direct a wire or needle into the breast so it resides at the already identified area of interest's location.
This patent disclosure covers methods of wire and/or needle guidance into the breast using breast tomosynthesis imaging technology. It covers both upright and prone biopsy equipment.
Tomosynthesis (tomo) is a method of performing three dimensional (3D) breast x-ray imaging. It generates images of cross sectional slices through a compressed breast, and also is used to identify breast pathologies. One of the advantages of tomosynthesis is that the images are three-dimensional, so that once an area of interest is identified in an image, its exact 3D coordinate in the breast can be calculated or estimated, e.g. from the x, y coordinate in the image of a slice and from the z, or depth, coordinate given by the image slice depth location. Another advantage of tomosynthesis is its ability to provide high contrast visibility of objects by the suppression of images from objects at different heights in the breast. Because of its superior contrast visibility, it is expected that there will be pathologies seen on the tomo images that will not be visible using standard x-ray mammography or stereotactic devices or using ultrasound or even MRI or other methods currently employed to provide guidance to the insertion of wires and needles to the location of an identified area of interest. For this reason, it is desired to develop localization methods using tomosynthesis systems that utilize tomosynthesis' natural 3D localization abilities.
This patent disclosure addresses both systems and methods for tomosynthesis imaging, and devices and methods for needle and wire localization using tomosynthesis imaging systems. In one non-limiting example, the new approach described in this patent disclosure is based on conventional tomosynthesis designs, e.g. as described in U.S. patent application Ser. No. 10/305,480, filed Nov. 27, 2002, now U.S. Pat. No. 7,123,684, issued Oct. 17-2006, U.S. patent application Ser. No. 10/723,486, filed Nov. 26, 2003, now U.S. Pat. No. 7,831,296 issued Nov. 9, 2010, U.S. Provisional Patent Application Ser. No. 60/628,516, filed Nov. 15, 2004, International PCT Application Serial No. PCT/US2005/0491941, filed Nov. 15, 2005, published as WO/2006/055830 on May 26, 2006, U.S. Provisional Patent Application Ser. No. 60/631,296, filed Nov. 26, 2004, and International PCT Application Serial No. PCTIUS2005/042613, filed Nov. 23, 2005, published as WO/2006/058160 on Jun. 1, 2006, which are hereby incorporated by reference. Typically, the breast is compressed between a breast platform and a compression paddle. The paddle may be one of the standard paddles used for screening mammography, or one with holes and guide marks used for needle localization or biopsy procedures with conventional mammography equipment, e.g. as described in U.S. Pat. No. 5,078,142 filed Nov. 21, 1989, U.S. Pat. No. 5,240,011 filed Nov. 27, 1991, U.S. Pat. No. 5,415,169 filed Feb. 17, 1993, U.S. Pat. No. 5,735,264 filed Jun. 7, 1995, U.S. Pat. No. 5,803,912 filed Apr. 25, 1995, U.S. Pat. No. 6,022,325 filed Sep. 4, 1998, U.S. Pat. No. 5,289,520 filed Oct. 6, 1992, U.S. Pat. No. 5,426,685 filed Jan., 24, 1994, U.S. Pat. No. 5,594,769 filed May 9, 1995, and U.S. Pat. No. 5,609,152 filed Feb. 15, 1995, which are hereby incorporated by reference, and as used in the prone or upright needle biopsy devices commercially available from the Lorad Division of Hologic, Inc. of Bedford, Mass. The x-ray tube is mechanically designed so that it moves along a path that images the breast from differing angles, making a sequence of exposures at differing locations along the path. A digital x-ray image receptor acquires the images. The detector can be stationary during the scan, or it can move during the scan such as if it was mounted on a c-arm connected with the x-ray tube or is otherwise connected to move in sync with the x-ray tube, though not necessarily through the same angle. The entire system can be oriented so that the patient is either upright or lying on a table with her breast pendulant and protruding through a hole in the table and positioned properly on the detector to access the area of interest as needed. One system design would be using a relatively small field of view, such as approximately 5×5 cm. This would correspond to developing a tomosynthesis biopsy system with similar field of view to standard prone table stereo localization systems. However, another way disclosed here, which differentiates a tomo biopsy system from conventional stereo localization system, is to use a significantly larger detector field of view. In one example of an embodiment the field of view can be at least 10×10 cm, in another at least 20×25 cm, in another approximately 24×29 cm.
Localization of an area of interest can start with breast acquisition carried out in a standard way used in breast tomosynthesis. The data is reconstructed, and reviewed. The area of interest is identified either on the reconstructed images of slices, or in the raw projection images. The 3D coordinates of the area of interest can be computed or estimated from the identification of the area of interest on the images.
Once the 3D location of the area of interest is calculated, known methods of directing needles and wires to that location can be used.
There might be some differences in tomo scans during biopsy procedures from screening mammography. The dose might be higher, to get lower noise images. The angular range might be wider or shallower, and the number of projections might be larger or smaller. One might want a wider angle, for example, to get higher precision depth discrimination. One might also want higher resolution for these scans, compared to conventional tomo screening. This could be accomplished through the use of smaller pixel sizes.
A biopsy system used with a tomosynthesis system can include a needle gun assembly with motorized or non-motorized stage that can direct a needle to a specific 3D coordinate in the breast. This stage may be swung or otherwise moved out of the way of the acquisition system during the initial tomosynthesis scan, so that if desired it does not shadow or interfere with the visualization of the breast or breast area of interest.
Following the tomo scan and the identification of the 3D area of interest location, the stage is moved into place. The needle is moved to the 3D coordinate previously identified. The needle may access in the breast via a left or right lateral access (e.g. with the needle roughly parallel to the compression paddle and the patient's chest wall), or it could access the breast with the needle roughly normal to the compression paddle, through an opening in the compression paddle. Or, the needle may enter the breast at an angle between the normal and parallel paths (in relation to the compression paddle and detector) through a hole in the breast compression paddle. It may also come from the front of the breast, directing the needle rearwards towards the chest wall. It can also come from between the paddle and the breast platform but at an angle rather than through the hole in the paddle.
The biopsy system should be capable of working with the tomosynthesis system in all orientations of the tomosynthesis system, including, but not limited to, CC, MLO, and ML and LM imaging orientations. These systems can rotate 360° around the breast and take images from any angle.
Standard techniques of breast biopsy typically involve verification of the needle's location before tissue sampling, known as pre- and post-fire verification. In pre-fire, the needle is inserted into the breast approximately 2 cm short of the center of the area of interest and x-ray exposures are made and images are generated and viewed to verify proper pre-fire needle location relative to the area of interest before tissue sampling. In post-fire, at least one additional exposure is made and the resulting image is viewed to verify proper needle location relative to the area of interest after the firing of the needle and before the tissue is sampled.
These verification images can be images from tomosynthesis scans, or they can be stereo x-ray pairs or individual images. The tomosynthesis scans can be done with different angular ranges and different number of projections and a different dose from conventional tomosynthesis imaging.
Post-fire needle verification can be accomplished in a variety of ways, which may depend on whether the needle access was lateral or tangential. One challenge arises from the fact that the gun and stage and needle are generally radio-opaque and can contribute artifacts to the images if not properly dealt with.
With tangential access, there may be an angular range where the gun and stage shadow the breast. Lateral access may not have the problem of the gun stage in the field of view, but it can have the needle in the field of view, and there might be other mechanics that if imaged can create image artifacts. In general, x-rays from angles that shadow the gun and stage are less useful. Solutions to this problem in accordance with the new approach disclosed in this patent specification include:                a. Development of needle and other sheathing materials that are sufficiently radiolucent that they will not create significant image artifacts. Possible materials are plastics, ceramics, glasses, carbon tubes, and low atomic number metals and other materials. If these materials are used, they can be marked with fiducial markings such as radio-opaque rings or dots allowing visibility in the tomosynthesis images so they can be differentiated from breast tissue or breast area of interest. Alternately, a needle can be used where only the tip (last 1-3 cm) is radiolucent and rest of the needle is radio-opaque.        b. Scanning through angles that do not shadow these objects. This can entail an asymmetric scan geometry, whereby all or an important part of the x-ray beam path does not pass through the needle or other radio-opaque parts. An example is scanning to just one side of the needle.        c. Scanning over a large range, and generally or always avoiding x-ray exposures when the stage or other radio-opaque parts shadow the breast, area of interest or image receptor. Alternatively, x-ray imaging can be done even in angular areas with this shadow problem, but these exposures can be eliminated from viewing or reconstruction, either automatically or through manual elimination via a user interface. Another alternate method involves artifact suppression algorithms used during reconstruction, as in known in tomosynthesis and CT scanning.        d. Stereotactic imaging. Conventional stereotactic imaging involves using a pair of x-ray images at, for example, ±15° to the normal to the compression paddle. This geometry involves sufficiently large angles to typically avoid the stage shadows on the image receptor. A tomo system can be used to take tomo projection images at angles that avoid undesirable shadows at relevant parts of the images.        e. Scan angle changes. A larger scan angle than used in conventional tomo imaging can better avoid artifacts from the stage.        f. Bringing the needle to a fixed distance from the lesion. An image can then be taken that does not obscure the area of interest, and the proper distance between needle and area of interest can be verified from imaging. The needle can then be advanced into the correct location within the area of interest based on information from the tomo or conventional imaging while the needle is spaced from the area of interest.        g. In many if not most cases the projection images and perhaps the reconstructed images of breast slices will contain at some location an image of the needle. The needle image can create artifacts in reconstructed images, which can be removed via artifact reduction algorithms as in known in conventional tomosynthesis and CT imaging. One algorithm can involve skipping projection images with extensive shadowing in the projections. Another algorithm can involve segmenting out the needle and other high contrast objects and avoiding reconstruction using these pixels, as has been used in CT and other imaging. Other alternatives include viewing the projection images, which can have images of the needles but no other significant artifacts.        
The examples of embodiments disclosed in this patent specification can include user interfaces to mark the area of interest location on either the projection tomo images or the reconstructed tomo images of breast slices. Signals directing the needle to the correct location in the breast can be generated automatically based on identifying the location of the area of interest in the images, or the coordinates of the area of interest can be displayed and the needle can be guided to the appropriate location under manual control.
For the pre and post fire images, a facility can be provided to mark the previously identified area of interest location on the current images. This can help visualization of proper needle placement, in case the area of interest becomes harder to see because it has been removed or in case the needle creates large artifacts. The orientation of the needle relative to this mark can provide assurance as to proper location placement.
The 3D nature of the tomosynthesis images allows for calculation of the 3D volume of the area of interest, once it has been identified on the tomosynthesis projections or reconstructed images of slices. This can be part of the display and used to help verify that the correct lesion has been targeted.